System for hydrogen generation through steam reforming of hydrocarbons and integrated chemical reactor for hydrogen production from hydrocarbons

ABSTRACT

The present invention provides a reactor, which includes:  
     a unitary shell assembly having an inlet and an outlet;  
     a flow path extending within the shell assembly from the inlet to the outlet, the flow path having a steam reformer section with a first catalyst and a water gas shift reactor section with a second catalyst, the steam reformer section being located upstream of the water gas shift reactor section;  
     a heating section within the shell assembly and configured to heat the steam reformer section; and  
     a cooling section within the shell assembly and configured to cool the water gas shift reactor section. The present invention also provides a simplified hydrogen production system, which includes the catalytic steam reforming and subsequent high temperature water gas shift of low-sulfur (&lt;100 ppm by mass) hydrocarbon fuels followed by hydrogen purification through the pressure swing adsorption (PSA). The integrated reactor offers significant advantages such as lower heat loss, lower parts count, lower thermal mass, and greater safety than the many separate components employed in conventional and is especially well-suited to applications where less than 15,000 standard cubic feet per hour of hydrogen are required. The improved system also may be started, operated and shut down more simply and quickly than what is currently possible in conventional systems. The improved system preferably employs active temperature control for added safety of operation. The hydrogen product is of high purity, and the system may be optionally operated with a feedback control loop for added purity.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an integrated chemical reactorfor the production of hydrogen from hydrocarbon fuels such as naturalgas, propane, liquefied petroleum gas, alcohols, naphtha and otherhydrocarbon fuels and having a unique unitized, multifunctionalstructure. The integrated reactor offers significant advantages such aslower heat loss, lower parts count, lower thermal mass, and greatersafety than the many separate components employed in conventionalsystems to achieve the same end. The integrated reactor is especiallywell-suited to applications where less than 15,000 standard cubic feetper hour of hydrogen are required.

[0003] The present invention also relates to the generation of hydrogenfor use in industrial applications, as a chemical feedstock, or as afuel for stationary or mobile power plants.

[0004] 2. Discussion of the Background

[0005] Hydrogen production from natural gas, propane, liquefiedpetroleum gas (LPG), alcohols, naphtha and other hydrocarbon fuels is animportant industrial activity. Typical industrial applications includefeedstock for ammonia synthesis and other chemical processes, in themetals processing industry, for semiconductor manufacture and in otherindustrial applications, petroleum desulfurization, and hydrogenproduction for the merchant gas market. The demand for low-cost hydrogenat a smaller scale than produced by traditional industrial hydrogengenerators has created a market for small-scale hydrogen productionapparatus (<15,000 standard cubic feet per hour (scfh)). This demand hasbeen augmented by the growing enthusiasm for hydrogen as a fuel forstationary and mobile powerplants, especially those employingelectrochemical fuel cells, which require hydrogen as a fuel.

[0006] Hydrogen is typically produced from hydrocarbon fuelsindustrially via chemical reforming using combinations of steamreforming and partial oxidation. This is typically achieved at scaleslarger than one ton per day using well-known process and catalystdesigns. For several reasons, it is difficult to adapt these large-scaletechnologies to economically produce hydrogen at small scales. Typicalindustrial applications produce far more than 15,000 standard cubic feetper hour (˜1 ton per day), and often employ catalytic steam reforming oflight hydrocarbons in radiantly-fired furnaces. Steam reforming ofhydrocarbons is illustrated for the simple case of methane below.

CH₄+H₂O→CO+3H₂

[0007] The above reaction is highly endothermic, and the reacting fluidmust have energy transferred to it for the reaction to proceed. Further,the extent of the reaction is low at low temperatures, such that greatlyelevated temperatures, often as high as 800° C., are required byconventional systems to convert an acceptable amount of hydrocarbon tohydrogen and carbon monoxide. The catalyst employed in industrialreactors is typically composed of an active nickel metal componentsupported on a ceramic support.

[0008] The radiantly-fired furnaces employed in large-scale industrialreactors have many disadvantages that make them unsuitable forsmall-scale systems. The most important disadvantage is the very hightemperature of the radiant burners and the gas contacting the reactorsurfaces, which are usually tubular in form. The temperature of theradiant burners often approaches or exceeds the melting temperature ofthe alloy from which the tubes are fabricated. Melting of the tubes isprevented by the rapid endothermic catalytic reaction inside the tubes.If, however, the catalyst fails due to carbon formation, sulfurpoisoning or other causes, then the tubes form what is referred to inthe literature as a “hot spot,” which greatly accelerates the failure ofthe reactor tube in question. In large-scale systems, careful monitoringand control of the furnace and tube temperatures as well asexceptionally rugged construction of the tubes makes the risks of hotspots acceptable. For systems producing below 1 ton per day, however,the complexity and cost of such safety measures can become prohibitive.Nonetheless, small-scale steam reformers utilizing radiant heat transferare known and described, for example, in U.S. Pat. No. 5,484,577 toBuswell. et al. The extreme measures necessary to control thetemperature in arrays of reformer tubes are likewise documented in U.S.Pat. No. 5,470,360 to Sederquist.

[0009] A means of transferring the necessary heat to the reacting gaseswithout radiant heat transfer and its attendant risks, which isespecially well-suited to small-scale steam reforming, is the use ofcompact heat exchange surfaces, such as arrays of tubes orfinned-plates. The heat transfer mechanism in such devices is dominatedby convection and conduction with minimal radiant transfer. An exampleof this approach is described in U.S. Pat. No. 5,733,347 to Lesuir,wherein finned plates are employed to increase heat transfer. Tubularcompact heat exchangers for steam reforming are sold by Haldor Topsoe,Inc. of Houston, Tex.

[0010] Conventional hydrogen generation systems employing steamreforming of hydrocarbon fuels typically include three main reactionsteps for producing hydrogen; steam reforming, high-temperature watergas shift, and low temperature water gas shift. The important reactionsfor methane are as follows:

CH₄+H₂O→CO+3H₂ steam reforming

CO+H₂O→CO₂+H₂ water gas shift

[0011] It is evident from the equation for steam reforming ofhydrocarbon fuel that the principal products are hydrogen and carbonmonoxide. The carbon monoxide may be converted into additional hydrogenvia a catalytic reaction with steam (water gas shift reaction.

[0012] The water gas shift reaction is mildly exothermic and thus isthermodynamically favored at lower temperatures. However, the kineticsof the reaction are superior at higher temperatures. Thus, it is commonpractice to first cool the reformate product from the steam reformer ina heat exchanger to a temperature between 350° C. and 500° C. andconduct the reaction over a catalyst composed of finely divided oxidesof iron and chromium formed into tablets. The resulting reformate gas isthen cooled once again to a temperature between 200° C. and 250° C. andreacted over a catalyst based upon mixed oxides of copper and nickel. Anexample of this approach is given in U.S. Pat. No. 5,360,679 to Buswell.et al. In cases where an exceptionally pure hydrogen product isrequired, the temperature of the low-temperature shift converter iscontrolled by including a heat exchanger in the reactor itself, and anexample of this approach is given in U.S. Pat. No. 5,464,606 to Buswell.et al. In all cases, the low temperature shift converter is quite largebecause of the poor catalyst activity at low temperatures.

[0013] In conventional systems, subsets of the process components areconnected to one another via external plumbing; each component of theprocess being typically referred to as a “unit process,” in the chemicalengineering literature. This approach is preferred in large, industrialunits because standard hardware may be used. Owing to the large size ofindustrial units, the unit process approach also makes shipping of thecomponents to the site of the installation feasible, as combinations ofthe components are sometimes too large to be transported by road orrail.

[0014] For systems producing less than 1 ton per day, however, the unitprocess approach has many disadvantages. The first disadvantage is thehigh proportion of the total system mass dedicated to the hardware andplumbing of the separate components. This high mass increases startuptime, material cost, and system total mass, which is undesirable formobile applications such as powerplants for vehicles.

[0015] Another disadvantage of the unit process approach in smallsystems is the complexity of the plumbing system to connect thecomponents. The complexity increases the likelihood of leaks in thefinal system, which presents a safety hazard, and also significantlyincreases the cost of the assembly process itself. Moreover, therequirement that each component have its own inlet and outlet provisionsalso adds considerable manufacturing cost to the components themselves.

[0016] A third disadvantage is the high surface area of the plumbingrelative to the unit process hardware itself, which means that adisproportionately large amount of heat is lost through the connectingplumbing in small scale systems. This can drastically reduce the thermalefficiency of the system and adds cost and complexity associated withadequately insulating the plumbing system.

[0017] A fourth disadvantage to the unit process approach in small-scalesystems is that this approach requires a large volume to package, aseach component and its associated plumbing must be accessible forassembly and maintenance purposes. This is particularly disadvantageousin space-sensitive applications such as building fuel cell powerstations, fuel cell vehicle refueling stations, and fuel cell mobilepowerplant hydrogen generation.

[0018] Hydrogen is typically separated from the other reaction productsusing pressure swing adsorption (PSA) technology. The design of thesePSA systems is largely dictated by the catalyst chemistry employed inthe steam reformer and the low-temperature water gas shift reactor.These catalysts, typically based on nickel metal in the former andcopper in the latter case, are extremely sensitive to poisoning anddeactivation by sulfur or molecular oxygen. Thus, the incoming feed gasmust be carefully treated to remove these materials. Further, the systemmust protect the catalysts against these agents during startup,shut-down, and during intervals when the system is shut down. Especiallyin the case of molecular oxygen, exposure of the active catalyst canlead to catalyst damage and even create a safety hazard throughpyrophoric oxidation of the finely-divided base metal catalysts.

[0019] Several steps are necessary in conventional systems to preventdamage to the reforming and Low Temperature Shift (LTS) catalysts.

[0020] (1) During operation, the incoming fuel must be treated to removeboth sulfur and molecular oxygen. Sulfur in particular is generallyreduced below 1 part per million, and more preferably below 100 partsper billion. This is typically achieved through a combination of apartial oxidation to remove oxygen followed by a hydrodesulfurization(HDS) process. Such systems typically require recycle ofhigh-temperature, hydrogen-rich product gas to the inlet through the useof a gas compressor or a fluid ejector as exemplified by U.S. Pat. No.3,655,448 to Setzer, U.S. Pat. No. 4,976,747 to Szydlowski and Lesieur,and U.S. Pat. No. 5,360,679 to Buswell. et al. Because accuratetemperature control is required for the HDS reaction, several heatexchangers as well as active temperature control logic circuits and flowcontrol valves are also required. Provision of these reactors, heatexchangers, valves, as well as sensors and controls adds significantlyto the complexity of conventional systems.

[0021] (2) Startup of conventional system requires bringing all of thecomponents to near operating temperature, usually while blanketed ininert gas, then carefully initiating the reaction. Before the system isat operating conditions, full removal of sulfur and molecular oxygen isnot guaranteed, so the process feed gas must be vented to theatmosphere, wasting fuel, generating air pollution, and creating apotential safety hazard while further increasing system complexity.Because the added components for fuel pretreatment add significant massto the system, they also extend the warmup time required for hydrogenproduction. In situations with a variable hydrogen demand, this cancreate a need for extensive onsite hydrogen storage to supply thehydrogen demand while the system reaches operating conditions.

[0022] (3) During shutdown and periods when the conventional system isnot operating, the reaction system is typically purged with inert gasesunder pressure. Alternatively, substantially leak-tight valves must besupplied to prevent ingress of atmospheric air to the unit with theresultant catalyst deactivation/damage.

[0023] For large-scale applications the added cost/complexity of theconventional systems does not adversely affect the system economics.When this traditional approach is applied to small-scale systems,however, the relative cost of these added components becomesdisproportionately large, and the resulting hydrogen cost is dominatedby the cost of the system. Accordingly, it is not advantageous to simplyscale down large scale systems if a small scale system is desired.

[0024] Conventional steam reformer systems for natural gas and otherlight hydrocarbons fall into two broad classes. In the first, thereactors are operated at or near ambient pressure at low temperatures(typically less than 650° C.). This is typical of conventional systemsdesigned for small-scale applications producing impure hydrogen. Forpure hydrogen to be produced, the reformer product must be compressed tohigh pressure for subsequent cleanup via PSA, metal separationmembranes, or other conventional techniques. Because steam reformingcreates additional moles of gas, the compression of the product gas isvery energy-intensive and requires expensive and complicated compressionand intercooling equipment. The second class of reformers is typicallyused in large-scale applications and is operated at high pressures(often above 20 bar). Because of the thermodynamics of the steamreforming reaction, these high pressure reactors must be operated atmuch higher temperatures, often approaching 900° C., to attain adequateconversion of the hydrocarbon fuel to hydrogen. The higher temperaturesand pressures require the use of more expensive materials ofconstruction than are employed in the low-pressure systems, but this ismore than offset by the reduction in reactor volume obtained due toenhanced chemical reaction rates. Unfortunately, in small-scale systems,the provision of compression and pumping equipment to deliver thereactants into a high-pressure (20 bar or higher) reactor canundesirably increase the cost of such a system.

[0025] Conventional pressurized steam reformer systems often areoperated with very high temperatures in the combustion products used toheat the endothermic reaction zone. This high temperature allows areduction in the amount of heat transfer area required to complete thereaction, and thus a reduction in reformer cost. Often, the mode of heattransfer to the wall of the tubes in the conventional reformers is acombination of radiation and convection, with the combustion carried outin a conventional premixed or diffusion-flame burner. The operation ofthe primary steam reformer with such high gas temperatures can lead tosignificant excursions in the reformer tube wall temperature due eitherto poor control of the distribution of the hot gases or to poisoning ofthe reforming catalyst. If the catalyst for the endothermic steamreforming reaction is locally-poisoned, the heat flux from thecombustion products to the wall can form a local “hot spot.” In eithercase, the increase in the reformer wall temperature can lead topremature reformer structural failure, presenting both a safety and anoperational liability.

[0026] Conventional systems for hydrogen generation through steamreforming of hydrocarbons have several inherent deficiencies which makethem ill-suited to economical small-scale hydrogen production. The firstis the requirement for strict control of sulfur and molecular oxygenconcentrations in the steam reforming and LTS reactors. The secondconcerns the problems with operation in the ambient pressure regimewhere the large volume of reformate gas must subsequently be compressedprior to purification. The third is associated with operating thereactor in the high-pressure regime typical of large-scale units whereappropriate compression and pumping equipment adds considerable cost atsmall scales. The final shortcoming is the risk of overheating the steamreforming reactor structure due to the very high gas temperaturesemployed in the combustors in conventional systems and their reliance onradiant heat transfer, especially in high-pressure systems as employedin large-scale applications.

[0027] It has been recognized previously that integrating the elementsof the unit process more closely beneficially reduces heat losses andimproves compactness. U.S. Pat. No. 5,516,344 to Corrigan describes asteam reforming system wherein the unit process elements are integratedinto a common mounting rack having a reduced requirement for insulationand having improved compactness. This approach, however, undesirablyretains the multiple connections and extensive plumbing characteristicof the unit process approach. Moreover, because of its complicatedpackaging, the assembly of the Corrigan system undesirably presents asignificant challenge.

[0028] Another attempt at improving compactness is described in U.S.Pat. No. 5,733,347 to Lesieur, wherein the primary reforming reactor andthe catalytic burner are integrated into a planar reactor with compactheat transfer surfaces. This reactor requires separate heat exchangersto cool the gas after the primary reformer, as well as separate reactorsfor the water gas shift. These all require interconnections, as do thearray of planar reactors envisioned by Lesieur. These connections onceagain present the same drawbacks found in unit process reactor systems.

SUMMARY OF THE INVENTION

[0029] Accordingly, one object of the present invention is to provide areactor for hydrogen production that avoids the problems associated withconventional systems.

[0030] Another object of the present invention is to provide a reactorfor hydrogen production that is suitable for applications where lessthan 15,000 standard cubic feet per hour of hydrogen are required.

[0031] Another object of the present invention is to provide a reactorfor hydrogen production that is safer and more cost efficient thanconventional systems.

[0032] Another object of the present invention is to provide a reactorfor hydrogen production that is less complex and is more space-sensitivethan conventional systems.

[0033] Another object of the present invention is to provide for theproduction of hydrogen from a hydrocarbon fuel such as natural gas,propane, naphtha, or other hydrocarbons low in sulfur content (<100 ppmsulfur by mass).

[0034] Another object of the present invention is to produce hydrogenwhich is substantially pure (>99.99%) by separating impurities using apressure swing adsorption (PSA) system.

[0035] Another object of the present invention is the provide for theelimination of the pretreatment of the fuel feed to the steam reformerfor the removal of sulfur and molecular oxygen.

[0036] Another object of the present invention is the provide for theoperation of the system in a mesobaric regime, between 4 and 18atmospheres, where appropriate fluid compression devices of smallcapacity, low cost, high efficiency and high reliability are readilyavailable, and the resultant thermal efficiency of the hydrogenproduction system is very high.

[0037] Another object of the present invention is to provide for thefeedback control of the delivery of fuel and/or air to a catalyticcombustor in proportions such that the peak temperature of the gasesentering the primary steam reformer does not exceed a safe maximumtemperature determined by the metallurgy of the steam reformer.

[0038] Another object of the present invention is to provide for theoperation of a steam reforming system without a low temperature watergas shift reactor.

[0039] Another object of the present invention is to provide for theoperation of a hydrogen production system with feedback control ofproduct carbon monoxide content.

[0040] Another object of the present invention is to provide a processhaving a simplified system construction, operation, and controlresulting in low cost and relatively fast start-up and shut-down.

[0041] These and other objects have been achieved by the presentinvention, the first embodiment of which provides a reactor, whichincludes:

[0042] a unitary shell assembly having an inlet and an outlet;

[0043] a flow path extending within the shell assembly from the inlet tothe outlet, the flow path having a steam reformer section with a firstcatalyst and a water gas shift reactor section with a second catalyst,the steam reformer section being located upstream of the water gas shiftreactor section;

[0044] a heating section within the shell assembly and configured toheat the steam reformer section; and

[0045] a cooling section within the shell assembly and configured tocool the water gas shift reactor section.

[0046] Another embodiment of the present invention provides a reactorfor the production of hydrogen from at least one selected from the groupincluding natural gas, propane, liquefied petroleum gas, alcohols,naphtha, hydrocarbon fuels and mixtures thereof, the reactor including:

[0047] a unitary shell assembly having an inlet and an outlet;

[0048] a flow path extending within the shell assembly from the inlet tothe outlet, the flow path including a convectively-heated catalyticsteam reformer and a convectively-cooled water gas shift reactor.

[0049] Another embodiment of the present invention provides a method forproducing hydrogen, which includes:

[0050] feeding at least one fuel selected from the group includingnatural gas, propane, liquefied petroleum gas, alcohols, naphtha,hydrocarbon fuels and mixtures thereof, into a reactor which includes aunitary shell assembly having an inlet and an outlet, and a flow pathextending within the shell assembly from the inlet to the outlet, theflow path including a convectively-heated catalytic steam reformer and aconvectively-cooled water gas shift reactor, whereby hydrogen isproduced.

[0051] Another embodiment of the present invention provides a method forproducing hydrogen from at least one fuel selected from the groupincluding hydrocarbon fuel, natural gas, propane, naphtha, hydrocarbonswith <100 ppm sulfur by mass, and mixtures thereof, which includes:

[0052] producing hydrogen by steam reforming the fuel; and

[0053] substantially purifying said hydrogen with a pressure swingadsorption (PSA) system;

[0054] wherein prior to the producing, no pretreatment of the fuel toremove at least one impurity selected from the group including sulfurand molecular oxygen and mixtures therof is carried out.

BRIEF DESCRIPTION OF THE FIGURES

[0055] Various other objects, features and attendant advantages of thepresent invention will be more fully appreciated as the same becomesbetter understood from the following detailed description whenconsidered in connection with the accompanying drawings in which likereference characters designate like or corresponding parts throughoutthe several views and wherein:

[0056]FIGS. 1a and 1 b are schematics of two preferred embodiments ofthe reactor flow geometry on both the tube and shell sides.

[0057]FIG. 1b differs from FIG. 1a in that it has an integral catalyticburner.

[0058]FIG. 2 shows a preferred embodiment of the reactor of the presentinvention without an internal catalytic burner and without extendedsurfaces on the tubes in the tubular array, which is provided withbaffles to create a multi-pass cross-flow geometry in the shell sidefluid pathway.

[0059]FIG. 3 shows a preferred embodiment of the reactor of the presentinvention with plate fin heat exchange surfaces attached to the tubes onthe shell side and an adiabatic water gas shift reactor zone placedafter the convectively cooled water gas shift reactor zone. This figurealso illustrates the preferred combination of extended tube surfaces andbaffles.

[0060]FIG. 4 shows a preferred embodiment of the reactor of the presentinvention without baffles, and with shell side extended surfacecomprising loose packing material. This figure also shows onemanifestation of a catalytic burner included within the reactor shell.FIG. 4 also depicts an outer housing and insulation system.

[0061]FIG. 5 is a schematic of the hydrogen production system of apreferred embodiment of the present invention.

[0062]FIG. 6 is a logic diagram for a preferred combustor outlettemperature control apparatus of the present invention.

[0063]FIG. 7 is a logic diagram for a preferred gas purity controlapparatus of the present invention.

[0064]FIG. 8 illustrates a computer system upon which a preferredembodiment of the present invention may be implemented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] Various other objects, features and attendant advantages of thepresent invention will be more fully appreciated as the same becomesbetter understood from the following detailed description of thepreferred embodiments of the invention.

[0066] Preferably, according to one embodiment of the present invention,an integral reactor for the production of hydrogen from natural gas,propane, liquefied petroleum gas, alcohols, naphtha and otherhydrocarbon fuels and mixtures thereof is provided where severalcomponents of the process system are combined into a single mechanicalstructure. These components will preferably include aconvectively-heated catalytic steam reformer, a cooler for the reformateproduct from the steam reformer and a convectively-cooled water gasshift reactor. The reactor may additionally and optionally include apreheat section to heat the inlet feeds. The packing of this preheatsection may additionally and optionally serve as a sulfur absorbent bed.The reactor may additionally and optionally include an adiabatic watergas shift reactor appended to the exit of the convectively cooled watergas shift reactor.

[0067] Preferably, the reactor of present invention includes a tubulararray wherein the fuel and water to be reformed flow through the tubes,and the cooling and heating fluids flow outside the tubes, with a singlereforming side inlet tube header and a single reforming side outlet tubeheader. The interior of these tubes is preferably provided with acatalyst in the form of a coating, a monolith, or as a loose packing ofpellets, extrudates or the like. Preferably, the reactor also includes ashell assembly, with a means of thermal expansion relief, one or moreinlets for a cooling medium for the water gas shift reactor, and one ormore outlets for the hot combustion product. The reactor shell assemblymay additionally and optionally have one or more outlets for heatedcoolant for the water gas shift reactor and one or more inlets for thehot combustion product to heat the steam reforming reactor.

[0068] Preferably, the reactor tube array surface area may be enhancedon the shell side of the tubes for the purposes of aiding heat transferbetween the shell side fluid and the tube walls. The surfaceaugmentation may be accomplished through the use of twisted tubes,finned tubes, rifled tubes, plate fins, by means of a loose packingmaterial, or by other means apparent to one skilled in the art.

[0069] Another preferred embodiment of the invention provides that thefluids flowing outside the tubes in the shell side may be forced to flowacross the tubular array, substantially normal to the axis of the tubes,by baffles. These baffles may be employed with or without the surfacearea enhancements which are another embodiment of the present invention.

[0070] Another preferred embodiment of the present invention providesthat a catalytic burner may be incorporated in the shell side of thereactor assembly. This catalytic burner may be provided with one or moreinlets for fuel delivery. This burner may also be provided with a meansof mixing the fuel and heated air. This burner may also be provided witha means of preheat and/or ignition. This burner may also be providedwith one or more temperature sensors.

[0071] Preferably, the steam reforming catalyst is resistant topoisoning by sulfur and molecular oxygen.

[0072] Preferably, the water gas shift catalyst is resistant topoisoning by sulfur.

[0073] Preferably, the reactor includes an outer housing and insulationassembly.

[0074] Referring to FIG. 1a, one embodiment of the overall flow geometryof the reactor of the present invention is provided with an inlet on thetube side for entry of vaporized, mixed water and fuel, which flowthrough a first region packed with steam reforming catalyst, wherecatalytic steam reforming takes place, and a second region packed withwater gas shift catalyst, where the water gas shift reaction takesplace, after which the reformed gases exit the reactor. A second fluidstream enters the shell side near the outlet of the tube side, and flowsgenerally in counterflow to the reformate flowing through the tube side.This second fluid stream is lower in temperature than the exitingreformate, and it removes heat from the water gas shift portion of thetube side of the reactor. In the embodiment of FIG. 1a, the heated airthen exits the shell side through an outlet port and is conveyed to anexternal catalytic combustor, where the heated air is mixed with one ormore fuel streams and combusted over a catalyst or in a conventionalburner. The hot combustion product is then returned to the shell side ofthe reactor, where the hot combustion product convectively heats thelower temperature reformate in the steam reformer section of the tubeside.

[0075] Another preferred embodiment of the overall flow geometry of thepresent invention is shown in FIG. 1b, which differs from that of FIG.1a in that the catalytic combustor is located within the shell side ofthe reactor. In the embodiment of FIG. 1b, the fuel for the combustor isintroduced into the shell-side fluid flow, and the fuel-air mixture iscombusted on a catalyst, which is located inside the reactor shell andintimately in contact with the reactor tube walls.

[0076] Referring to FIG. 2, the preferred reactor of the presentinvention has an inlet for mixed, pre-vaporized fuel and steam 1, whichcommunicates with a plenum 2, which distributes the mixture to the arrayof reactor tubes 3. These reactor tubes are mounted to the inlet tubeheader 4 by welding, brazing, swaging or other processes capable ofcreating a leak-tight joint in the materials of construction. Mostpreferably, the reactor tubes 3 are joined to the inlet header 4 bybrazing or welding. The reactor tubes are provided, as is illustrated inthe cut-away view of FIG. 2, with a charge of steam reforming catalystmaterial 5. This catalyst material 5 may be a loose packing asillustrated, or may be a catalytic coating, or may be a section ofmonolithically-supported catalyst. Such coated, packed bed, ormonolithic catalyst systems are well known to those skilled in the art.The reactor tubes are also provided with a water gas shift catalyst 50,which is located downstream from the steam reforming catalyst, 5. Thetubes 3 are further joined to a outlet tube header 6 by processessimilar to those for attaching the tubes to the inlet header 4. Theoutlet tube header 6 communicates with an outlet plenum 7, whichdelivers the reformate 2 product to an outlet port 8. The reactor tubes3 pass through holes in one or more baffles 9, which share the samegeometrical pattern of holes as the inlet and outlet headers 4 and 6.The spacing between these baffles is governed by the allowable pressuredrop and required heat transfer rate on the shell side of the reactor.The baffle spacing may be different in various portions of the reactor.The baffles 9 shown in FIG. 2 are chorded to allow fluid to flow aroundthe end of the baffle and along the tube axis through a percentage ofthe cross-sectional area of the shell. The baffles are chorded between50% and 10%; more preferably they are chorded between 40% and 15%, mostpreferably they are chorded between 30% and 20%. The direction of thechorded side alternates by 180 degrees such that fluid is forced to flowsubstantially perpendicular to the long axis of the tubes 3. Alternativebaffle designs are apparent to one skilled in the art and are includedwithin the scope of the present invention. Preferred examples ofalternative baffle designs include baffles chorded in more than onelocation, circular baffles of alternating ring and circle shapes, andwedge-shaped baffles.

[0077] The baffles fit with a close tolerance to allow a sliding fit tothe shell assembly 10. The shell assembly is secured to either one orboth of the inlet and outlet headers by welding, brazing, swaging, orother methods which are apparent to one skilled in the art. The closetolerance fit between the baffles and the shell is chosen such that thebaffles will not bind against the shell wall during assembly andoperation while still minimizing leakage between the baffles and theshell wall. If the shell 10 is rigidly secured to both headers it isespecially preferable to provide a means for relative thermal expansionand contraction between the reactor tubes and the shell to occur withoutundue restraint. In FIG. 2 thermal expansion is provided for by acorrugated tube or bellows 11. If the shell is fixed to only one header,relative expansion may be provided for with a sliding fit and sealsystem between the shell bore and the outer surface of the other reactorheader to minimize leakage while allowing free thermal expansion of thetubular array. Other means of providing free thermal expansion of thetube array will be apparent to one skilled in the art, and are includedwithin the scope of the present invention.

[0078] The reactor of FIG. 2 employs the overall flow geometry of FIG.1a, and is thus provided in the shell-side of the water gas shiftsection with a cold air inlet 12 as well as a hot air outlet 13. Most ofthe shell-side air is prevented from bypassing the hot air outlet 13 byan unchorded baffle 14, which fits snugly against the shell assembly 10inner wall. The reactor is further provided in the shell side of thesteam reforming section with a hot combustion product inlet 15 and acooled combustion product outlet 16. The inlets and outlets are depictedas single tube sections in FIG. 2, but it must be understood that otherinlet and outlet types are possible, including ring manifolds andmultiple tube fittings. Such alternative embodiments may beadvantageously employed to reduce thermal stresses in the tubes, tomodify heat transfer characteristics, or for other purposes apparent toone skilled in the art.

[0079] The reactor of FIG. 2 is provided with an external burnerassembly 18. In the embodiment of FIG. 2 this burner assembly is acatalytic burner with catalyst zone 22, and it will be understood thatalternative burner designs are known in the art which employ premixed ordiffusion burning or combinations thereof. Other preferable types ofburners are also apparent to one skilled in the art, and it is intendedthat the choice of external burner shall not limit the reactor of thepresent invention. The external burner assembly 18 is provided with atleast one fuel injection port 19. The air inlet may additionally beprovided with at least one air preheater element 23. This preheaterelement may alternatively be replaced or augmented with a pilot light, aspark ignitor, or an electrically heated catalyst. These and othermodifications to the burner assembly are apparent to one skilled in theart.

[0080] The tubes 3 are preferably filled with at least two catalystsystems. In the steam reforming zone, a catalyst 5 active for steamreforming is used, while in the water gas shift zone a catalyst 50active for water gas shift but substantially inactive for methanation isemployed. These catalyst systems may be in the form of surface coatings,a packed bed of loose particles, or as a monolithically-supportedcatalyst of the shape of the inside of the tubes. Most preferably thecatalyst is either coated or is in the form of a packed bed. In FIG. 2,the catalyst is a packed bed of loose particles retained between theinlet and outlet headers by catalyst support screens 17. Prior to thesteam reforming zone, a zone of chemically inert packing may be providedas a heat transfer media only. In this configuration, the reactants maybe preheated in order to bring their temperature to a level where thecatalytic steam reforming reaction occurs at a meaningful rate. Anpreferred embodiment of the present invention replaces the inert packingin this preheat zone with a sulfur absorbent such as zinc oxide. Thissulfur absorbent can serve as a guardbed to protect the steam reformingcatalyst from poisoning by sulfur.

[0081] In a preferred embodiment, the steam reforming catalyst iscapable of operation in the presence of less than 100 ppm of sulfur bymass in the fuel feed and is insensitive to the presence of molecularoxygen in the fuel feed. More preferably, the catalyst is capable ofbeing shut down from operation and restarted without the use of reducingor inert gas. Most preferably, the catalyst active metal is chosen fromone or more of those in group VIIIB of the periodic table, incorporatedherein by reference. Examples of the preferred metals are ruthenium,rhodium, iridium, platinum and palladium. These metals are preferablysupported on a ceramic support of high surface area. Preferred examplesof supports are oxides of aluminum, zirconium and magnesium, as well asmixed oxide spinels such as calcium aluminate, nickel aluminate ormagnesium aluminate. Other ceramic supports will be apparent to oneskilled in the art and are included in the scope of the presentinvention.

[0082] In a preferred embodiment, the water gas shift catalyst iscapable of operation in the presence of less than 100 ppm of sulfur bymass in the fuel feed and can be started in the presence of partiallyreacted mixtures of fuel and water, i.e. reformate from the steamreforming reactor. The catalyst also preferably does not require inertgas for shutdown. An example of a preferred catalyst is a finely dividedmixture of oxides of iron and chromium, marketed as high temperaturewater gas shift, or “ferrochrome” catalyst. A second example of apreferred catalyst includes platinum supported on aluminum oxide, withor without promotion by oxides of cerium or other metal oxides.

[0083] Referring to FIG. 3, a preferred embodiment of the reactor of thepresent invention is depicted which employs both baffles 9 as in FIG. 2as well as extended heat exchange surfaces on the outer walls of thereactor tubes 3. In this case, a plurality of closely-spaced plate fins20 are provided. These fins may be bonded to the reactor tube bybrazing, or more preferably by hydraulically expanding the tubes 3 intoclose contact with the plate fins 20. The plate fins, like the baffles9, also have a pattern of holes which is identical to that in the inletand outlet headers.

[0084]FIG. 3 also shows an adiabatic water gas shift reactor 21 appendedto the outlet tube header 6. This reactor increases the volume ofcatalyst accommodated without increasing the usage of the expensivemetal alloy reactor tubing. The additional catalyst volume can be usedto better approach the equilibrium conversion of the water gas shiftreaction at the outlet temperature conditions. This is typically desiredwhen the outlet temperature of the reformate from the water gas shiftreactor is below 400° C.

[0085]FIG. 4 shows a preferred embodiment of the reactor of the presentinvention wherein the overall flow geometry is that of FIG. 1b. In thisembodiment the shell side is packed with a loose packing material toprovide extended surface area for the tubes 3. It should be understoodthat other types of extended surfaces are possible, such as finnedtubes, rifled tubes, twisted tubes, and combinations thereof. All ofthese eliminate the possibility of using baffles in conjunction with theextended surface area, whereas plate fins and loose packing do not. Itshould be noted that in the embodiment of FIG. 4 baffles are notemployed, and the overall flow is substantially parallel to the axis ofthe tubes 3. The embodiment of FIG. 4 also includes a catalytic burnerintegrated within the reactor shell. The catalytic burning isaccomplished by a zone of packing 29 which is catalyzed with anappropriate combustion catalyst, such as mixtures of palladium andplatinum supported on a ceramic support. The size of this catalyzed zoneis chosen to meet the requirements of the specific application, and mayfill the entire reactor shell above the unchorded baffle 14.Alternatively, the unchorded baffle 14 may be omitted, and the heatedair from the water gas shift zone may proceed directly to the steamreforming zone where catalytic combustion will occur.

[0086] Near the shell side inlet 15 to the catalytic combustion zonethere is a fuel distribution assembly 24, which allows fuel to beintroduced into the catalytic combustion zone. Alternatively, andpreferably, the combustion zone may be provided with more than one fueldistribution assembly 24, which may be employed to control thetemperature profile in the combustion zone. It should be understood thatany number of configurations for this fuel distribution assembly arepossible and may be employed in the reactor of the present invention.The one or more fuel distribution assemblies 24 are provided with a fuelfeed controller 25, and the reactor is provided with at least onetemperature sensor 26 to be used in control of the combustiontemperature. The temperature sensor 26 is illustrated as located at theshell of the reactor, but may be alternatively located in a thermowelllocated in a reaction tube or at other locations within the reactor. Theintimate contact between the catalyst and the reactor tubes allows verygood heat transfer, but makes temperature control more difficult aswell. Another preferred embodiment of the present invention replaces theloose, catalyzed packing with a catalyzed monolith provided with apattern of holes which are larger than the reactor tube outer diameters.This type of monolithic combustion catalyst, because it is aligned bythe shell assembly, and does not contact the reactor tubes, will poseless of a danger to overheating the reactor tubes and causing theformation of hot spots. Even if the monolithic combustion support didcontact the tube walls locally, hot spotting would be less likely ascombustion is distributed throughout the monolith volume, rather thanbeing localized only at the tube wall.

[0087]FIG. 4 also depicts an outer housing 27 that can be constructed toextend over the entire outer surface of the insulation system 28 or aportion thereof, and which is only depicted over a small segment of theinsulation system 28. The insulation system may be constructed from oneor more layers of insulation materials, and may be either rigid orflexible. The precise amount and type of insulation employed isdependent upon a variety of factors such as allowable heat loss, maximumsurface temperature of the outer housing 27, and the mode of structuralsupport for the reactor. These variables do not materially affect theperformance advantages of the reactor of the present invention, and anynumber of possible insulation configurations are considered within thescope of the present invention. The outer housing 27 also does notmaterially affect the operation of the reactor and is designed insteadbased upon factors such as structural requirements, environmentalconditions, and aesthetics. Thus, any number of configurations for theouter housing are considered within the scope of the present invention.

[0088] Several surprising and unexpected advantages of the reactor ofthe present invention are apparent when it is compared to theconventional systems.

[0089] The first advantage is the great simplification in theconstruction of the reactor system afforded by combining the steamreforming and water gas shift reactors and their associated heattransfer functionalities into a single mechanical device. Thiseliminates the requirement for separate inlet and outlet zones,fittings, and interconnecting plumbing. This advantage is even furtherevidenced in systems incorporating the feed preheat function and/or theinternal catalytic burner. In small hydrogen generation applications(<15,000 scf/hr or 1 ton per day), this reduction in physical componentsand interconnects can greatly reduce the cost of the completed system.

[0090] A second advantage is the great reduction in heat loss achievedby the reactor of the present invention when compared to the unitprocess approach of the conventional systems. In part because the numberof fittings and interconnecting plumbing is decreased in the novelreactor of the present invention, the amount of heat transfer surfacewith the ambient environment is greatly diminished. Consequently, theheat lost to the ambient environment is desirably proportionallyreduced. This heat loss can otherwise undesirably form a large energyrequirement in conventional small-scale, hydrogen-generating reactors.The reduction in heat loss achieved by the present invention leads to ahigher energy efficiency of the reactor and a faster warmup time.Additionally, the low heat loss of the reactor of the present inventionallows it to be maintained in a hot condition for extended periods oftime without generating hydrogen and without consuming much fuel, whichdesirably makes “hot standby” of the novel reactor more practical thanin conventional reactors.

[0091] A third advantage of the reactor of the present invention is itsability to start up from a cold condition more rapidly than conventionalreactors. This is believed to be due to both the lower structural weightof the reactor and its lower heat loss when compared to conventionaldiscrete reactors and heat exchangers. The rapid warmup capabilityallows the reactor of the present invention to be operatedintermittently without excessive penalties in warmup time or warmup fuelusage.

[0092] Preferably, the present invention is carried out withoutpretreatment of the fuel feed to the steam reformer for the removal ofsulfur and molecular oxygen. Pretreatments which are preferably excludedfrom the present invention include any or all of partial oxidation,hydrodesulfurization, adsorption, or absorption. Other such pretreatmentmethods known to one of ordinary skill in the art are preferablyexcluded as well.

[0093] Low-pressure water and hydrocarbon fuel are admitted to separateor combined fluid compression devices; and they are subsequently heatedto their vaporization points and admitted to a primary steam reformingreactor. This steam reforming reactor is provided with a catalyst whichis resistant to poisoning by both sulfur and molecular oxygen, and ispreferably based upon catalytically-active group VIIIB metals such asruthenium, rhodium, iridium, platinum, palladium or combinations thereofsupported on a ceramic support of high surface area. In this primarysteam reforming reactor, the vaporized fuel and steam are further heatedby a separate stream of hot combustion product which is separated fromthe reactants by the walls of the reactor, which also form heat exchangesurfaces. These heated gases are then encouraged to react by theaforementioned catalyst to form a hydrogen-rich product gas with acomposition near its equilibrium value at the reactor outlet conditions.This hydrogen-rich gas is then cooled and passed over a second catalystwhich is also sulfur resistant, and is active for the water gas shiftreaction while being substantially-inactive for the reverse of the steamreforming reaction, the methanation reaction. An example of such acatalyst is a finely divided mixture of oxides of iron and chromium,which is well-known in the art as “high temperature” water gas shift or“ferrochrome” catalyst. The hydrogen rich gas stream has much of itscarbon monoxide converted to carbon dioxide and hydrogen in the watergas shift reactor, and exits with a carbon monoxide concentrationbetween 0.3% and 4%, at a temperature above 200° C.

[0094] In conventional systems, a further low-temperature water gasshift reactor is provided, whereas in the system of the presentinvention no such reactor is provided, as an active, sulfur-tolerantcatalyst operable at such low temperatures is not easily made. Theproduct gas mixture is then further cooled either by heat exchange withambient air or cool water or by quenching with cool water in anevaporative cooler. Condensed water is then removed from the gas via aseparator, and the thus partially-dried gas mixture is admitted to thePSA purification system. In the PSA system, impurities are adsorbed fromthe gas while the product hydrogen is delivered at a high purity and atan elevated pressure (slightly below the steam reformer pressure). Theimpurities are then purged with a small portion of the hydrogen productat low pressure and are delivered as a fuel to a catalytic combustor,which is provided with an exit temperature sensor and a means ofcontrolling the rate of admission of air. The rate of air admission isthus controlled such that the exit temperature from the combustor isbelow the maximum allowable temperature of the reformer metallurgy. Thishot combustion product is then ducted to a heat transfer interface inthe steam reformer to provide heat for the endothermic reaction thereinto proceed. The combustion product, at a reduced temperature, may thenbe used to heat and vaporize the pressurized water and, if desired, fuelstreams.

[0095] As described below, the rate of air admission is controlled by afeedback loop based upon the outlet temperature of the catalyticcombustor. The calorific value of the low-pressure mixed fuel gasexpelled from the PSA system is determined by the degree of hydrogenpurity required. A feedback control system based upon a product carbonmonoxide sensor based on either infrared or electrochemical principleswill be used to set the rate at which the PSA system purges itself ofcontaminants. When high purity is desired, a high purge rate is employedand the calorific value of the low-pressure gases is high. When lessstringent purity is required, the rate of purging may be lower, and thecalorific value of the purged gases may be correspondingly lower.Indeed, the purge rate may be reduced to a point where the calorificvalue of the purge gas is too low to sustain the reactor temperature, atwhich point unreacted hydrocarbon fuel may be provided from a valve tomake up the deficit. Whereas the carbon monoxide concentration is ofspecial significance for fuel cell applications, in other applicationsit is understood that another impurity may be more critical, andfeedback based upon concentrations of that species may accordingly beemployed.

[0096] Referring to FIG. 5, the hydrogen production system of thepresent invention can process hydrocarbon fuels such as natural gas,town gas, refinery off-gas, propane, liquefied petroleum gas, naphtha,alcohols or any other hydrocarbon fuel with a sulfur content less than100 parts per million (ppm) by mass. Natural gas or liquified petroleumgas are preferred. More preferably, the sulfur content is less than 75ppm, most preferably, the sulfur content of the fuel is less than 50ppm. The second feed to the system is water, which is subsequentlychemically reacted with the fuel to yield hydrogen. This water feed mustbe conditioned to remove particles, organics, and ionized species. Thismay be achieved using methods apparent to one skilled in the art. Themolar ratio of the water to the fuel is such that the ratio of watermolecules to carbon molecules is between 2.5:1 and 8:1. More preferably,the ratio is between 3:1 and 5:1.

[0097] The water feed to the system is pressurized using an appropriatepump 66 to a pressure greater than the operating pressure of the system,which is preferably 4 atm to 18 atm. The pressurized water is thenadmitted to a heat exchanger 84 where it is heated by a second fluid,which is the cooled combustion product exhausted from the steamreforming reactor hot side 60. It must be understood that this heatexchanger may include more than one individual unit, and thatalternative strategies may be employed to heat the feed water such as byremoving heat from the hot hydrogen-containing gas exiting the water gasshift reactor 62, or from other high temperature streams in the system.Irrespective of the exact arrangement of the heat exchange means,sufficient energy is transferred to the water to cause it to vaporizeand allow it to be mixed with the fuel at 56.

[0098] The fuel is pressurized using compressor 54. This device may be apump if the fuel is a liquid, and may also be replaced and/or augmentedby a steam ejector employing pressure energy stored in the vaporizedwater to pressurize the fuel. The fuel is mixed with the vaporized waterat 56. The resulting pressure of the mixed fuel and water preferablyexceeds that of the steam reforming reactor 58, which is between 4 atmand 18 atm. This requires that sufficient energy be imparted to one ormore of the fluids to maintain the resulting mixture in the vapor phaseat the steam reforming reactor inlet. This may require the addition ofan evaporator for a liquid fuel, or may be achieved through superheat ofthe vaporized water.

[0099] The steam reforming reactor includes a high pressure, cold side58 wherein is disposed a quantity of catalytically active material aswell as a lower pressure, hot side 60. The mixed, vaporized fuel andwater enter the cold side 58 and are heated by the hot combustionproduct which flows through the hot side 60. These fluids are preventedfrom mixing by the shared structure of the reactor, which forms a heatexchange surface, or a plurality of heat exchange surfaces. The pressureof the fluid in the cold side of the reactor is between 4 atm and 18atm. More preferably, the pressure is between 5 atm and 15 atm. Mostpreferably, the pressure is between 10 atm and 15 atm. The catalystdisposed in the cold side of the reactor is resistant to both theadsorption of sulfur compounds and oxidation by both steam and molecularoxygen. The catalyst preferably includes an active metal or mixturethereof supported upon a ceramic support material of high surface area.Preferably the catalyst active metal or metals is selected from thegroup VIIIB metals of the periodic table, incorporated herein byreference. Most preferably the catalyst active metal includes one ormore of the following group VIIIB metals singly or in combination;ruthenium, iridium, rhodium, platinum and palladium. The temperature ofthe reacting mixture is increased in the steam reformer. The exittemperature of the heated reformate, or hydrogen rich mixture, dependsupon the fuel, pressure, steam to carbon ratio and metallurgy of thereactor. The exit temperature from the cold side 58 is preferablybetween 500° C. and 900° C. More preferably, the temperature is between600° C. and 800° C. Most preferably, the temperature is between 700° C.and 800° C.

[0100] This heated reformate gas passes from the cold side 58 of thesteam reformer to the hot side 62 of the water gas shift reactor, partor all of which is cooled by cooler, lower pressure air flowing throughthe cold side of the water gas shift reactor 64. Like the steamreformer, the water gas shift reactor is thus provided with one or moreheat transfer surfaces for transferring heat between these two fluids.Alternatively, the hot gases may be partially or completely cooled tothe water gas shift reactor temperature before being admitted to its hotside 62. A catalyst active for water gas shift and inactive formethanation is disposed within the hot side of the water gas shiftreactor 62. This catalyst must also be resistant to poisoning by sulfurcompounds. An example of a commercially-available catalyst is a finelydivided mixture of oxides of iron and chromium which is formed intopellets or tablets. The gas exiting the water gas shift reactor hot side62 is preferably greater than 200° C. in temperature. More preferably,the gas is greater than 250° C. and less than 400° C. in temperature.Most preferably the gas is greater than 275° C. and less than 350° C.

[0101] The hot, hydrogen rich reformate is then passed through a cooler68. This is depicted in FIG. 5 as being cooled by cool external air froma fan. Alternatively, the cooling may be accomplished via a series ofheat exchangers including heating the water feed to the system andcooling with air. Alternatively, the reformate may be cooled by heatexchange with cool water. Alternatively, the reformate may be cooledthrough the use of an evaporative chiller using directly injected water.These embodiments may also be combined in a variety of configurationsapparent to one skilled in the art, which do not in any way limit thescope of the present invention. The reformate exits this cooler 68 at atemperature below 100° C. More preferably, the temperature is between80° C. and 25° C. Most preferably the temperature is between 60° C. and30° C. Because the reformate gas is pressurized, the cooling will causesome portion of the water vapor to condense. This condensed water vapor,and any condensed fuel residuals, is then removed in a condensateseparator 74.

[0102] The partially dried reformate is then admitted to the PressureSwing Adsorption (PSA) system 72. PSA systems are known to those skilledin the art. The PSA system 72 removes impurities from the reformate,thus delivering a substantially pure hydrogen product at a pressureslightly lower than the reactor pressure due to pressure drop. Thecontaminant species are purged from the PSA system 72 using some of thepure hydrogen product. This purge gas is rejected at lower pressure thanthe hydrogen is delivered as product. It is also possible to provide avacuum pump to reduce the pressure at which the low-pressure exhaust isrejected to thus improve the performance of the PSA system 72. Theaverage hydrogen purity may be controlled by varying the rate with whichthe beds in the PSA system 72 are purged. This rate of purging may becontrolled via a feedback loop of the present invention which isdescribed herein. The PSA product outlet may optionally be provided witha gas composition sensor 70 for use in the control of the system.

[0103] The low-pressure purged gases from the PSA system 72 are fed tothe catalytic combustor 78, where they are mixed with the process airwhich is compressed by the feed compressor 76, and heated by thereformate in the cold side of the water gas shift reactor 64. Thecatalytic combustor is provided with an inlet end and an outlet end,with a means of preheat or ignition, a charge of combustion catalyst,and an outlet temperature sensor. The flowrate of air delivered by thefeed compressor 76 is regulated such that the temperature of thecombusted mixture does not exceed the maximum temperature allowed by themetallurgy of the steam reformer. The strategy for this control isdisclosed later in this document. The system is also provided with anauxiliary fuel metering valve 82, which may deliver low-pressure fuel asshown, or may be required to deliver pressurized fuel, to match thepressure utilized in the combustion loop. This valve may be used todeliver fuel during system startup, and to augment the low-pressurereject fuel gas from the PSA system 72 if it is insufficient to supplythe steam reformer heat requirements.

[0104] The hot combustion product is delivered to the hot side of thesteam reformer 60, where it is cooled in exchanging heat with thereformate. It then flows through the water preheater 84 to transfer heatfor the purpose of vaporizing the reactants. After leaving the waterpreheater 84, the combustion product is sufficiently cooled to beexhausted to the atmosphere. This exhaust may be unrestricted, flowthrough a back-pressure regulator, or flow through a gas turbine orother work recovering device. Such modifications are included within thescope of the present invention.

[0105] Referring to FIG. 6, the preferred embodiment of the temperaturecontrol scheme for the reactor-combustor system is shown. The controlscheme employs a minimum of two temperature sensors shown in FIG. 5, thefirst temperature sensor 80 in the hotter outlet stream of the catalyticcombustor and the second temperature sensor 52 in the outlet stream ofthe colder, steam reforming side of the steam reformer. The temperaturesat these two points are preferably measured at repeated intervals, andtheir values are compared to target values.

[0106] If the combustor outlet temperature measured by the sensor 80 isabove the preset value, which is dependent upon the fuel, the steam tocarbon ratio, the reactor pressure, and the reactor design, then thetemperature of the heated reformate measured by sensor 52 is checked. Ifthis temperature is below the minimum value consistent with properperformance, then the flowrate of air to the combustor must be increasedand the cycle repeated. This change in the airflow may be affected by avariation in the compressor or blower speed, or by the application of athrottling valve. The air to fuel stoichiometry will always be fuel leanin the reformer system of the present invention in order to control thepeak temperature to a safe level. If the reformate temperature is abovethe minimum temperature, the flowrate of the auxiliary fuel must bechecked. If this flowrate is zero, then the air flowrate must beincreased and the cycle restarted. If the flowrate of auxiliary fuel isnot zero, then the flowrate should be decreased and the cycle restarted.

[0107] If the combustor outlet temperature does not exceed the maximumtemperature, then the reformate temperature must be checked. If thereformate temperature is above the minimum value, then all is well andno changes are required. The control system will then continue to cycleuntil something disturbs the steady-state condition. If, however, thereformate temperature is below the minimum value, the flowrate ofauxiliary fuel must be increased and the cycle repeated.

[0108] Other control strategies which achieve the twin aims ofmaintaining a maximum temperature in the combustion product and aminimum temperature in the reformate will be apparent to one skilled inthe art. Modifications to the control strategy of FIG. 6 designed toimprove the response of the system or to reduce oscillations about thesteady state condition may also be envisioned. These alternative andmodified control strategies are encompassed within the scope of thepresent invention.

[0109]FIG. 7 presents a preferred example of a feedback control strategyfor the PSA subsystem based upon the signal from a carbon monoxidesensor. If the carbon monoxide sensor detects a concentration above themaximum value, the purge rate for the PSA system is increased and thecontrol cycle is repeated. If the carbon monoxide concentration is belowthe maximum value, and above the minimum value, then no action is takenand the control cycle repeats. If the value is below the minimum valuethen the purge rate is decreased and the control cycle repeats. Theminimum contaminant concentration is determined by minimum allowablesystem efficiency, as running at arbitrarily high purge rates willgreatly reduce hydrogen recovery and thus system thermodynamicefficiency. As noted previously, the example of carbon monoxide, thoughparticularly suitable for fuel cell applications, is not limiting.Feedback control based upon the exit concentrations of other gases mayalso be employed, and is within the scope of the present invention.

[0110] The improved hydrogen generation system of the present inventionhas many advantages compared to conventional systems, especially forapplications requiring less than one ton per day of hydrogen.Preferably, the present invention is used in a reactor system producingless than 1 ton per day of hydrogen, more preferably less than ⅞ ton perday, and most preferably less than ¾ ton per day.

[0111] The improved system of the present invention eliminates partialoxidation of the fuel, sulfur removal (via hydrodesulfurization or otherprocesses), and low temperature water gas shift. These simplificationsreduce system cost relative to conventional systems by eliminatingcomponents. It also improves safety and durability by reducing thenumber of interconnections which may develop leaks in service.

[0112] The improved system of the present invention is capable ofquicker and simpler startup from a cold or idle condition. This is dueto several factors, including the reduced mass of the present system dueto the elimination of many components as well as the fact that therugged catalysts employed in the system of the present invention areinsensitive to fuel impurities which require bypassing the feed inconventional systems until full operating temperature is attained. Thestartup is further simplified as the rugged catalysts do not requireinert purging during startup. The rugged catalysts of the presentinvention also do not require special precautions on shutdown such asinert purging. This simplifies the design of the system further, thusreducing cost and improving safety.

[0113] The improved system of the present invention preferably operatesin a pressure regime where suitable pressurization equipment iscommercially-available and very inexpensive. Conventional systemsoperate either at low pressure in the steam reformer, with subsequentcompression of the reformate product at high cost and complexity, or atvery high pressures where small-scale compression equipment is notreadily available.

[0114] The improved system of the present invention preferably employsactive control of the reactor peak temperature. This temperature islimited to a value consistent with extended operation of the reformer.In conventional systems, the peak gas temperatures were often above anacceptable service temperature of the reactor structure, and if anyupset in the endothermic catalytic reaction took place the structuremight be badly overheated.

[0115] Any embodiment of the hydrogen production system of the presentinvention may be implemented on a computer system. FIG. 8 illustrates apreferred computer system 801 upon which an embodiment of the presentinvention may be implemented. The computer system 801 includes a bus 802or other communication mechanism for communicating information, and aprocessor 803 coupled with the bus 802 for processing the information.The computer system 801 also includes a main memory 804, such as arandom access memory (RAM) or other dynamic storage device (e.g.,dynamic RAM (DRAM), static RAM (SRAM), and synchronous DRAM (SDRAM)),coupled to the bus 802 for storing information and instructions to beexecuted by processor 803. In addition, the main memory 804 may be usedfor storing temporary variables or other intermediate information duringthe execution of instructions by the processor 803. The computer system801 further includes a read only memory (ROM) 805 or other staticstorage device (e.g., programmable ROM (PROM), erasable PROM (EPROM),and electrically erasable PROM (EEPROM)) coupled to the bus 802 forstoring static information and instructions for the processor 803.

[0116] The computer system 801 also includes a disk controller 806coupled to the bus 802 to control one or more storage devices forstoring information and instructions, such as a magnetic hard disk 807,and a removable media drive 808 (e.g., floppy disk drive, read-onlycompact disc drive, read/write compact disc drive, compact disc jukebox,tape drive, and removable magneto-optical drive). The storage devicesmay be added to the computer system 801 using an appropriate deviceinterface (e.g., small computer system interface (SCSI), integrateddevice electronics (IDE), enhanced-IDE (E-IDE), direct memory access(DMA), or ultra-DMA).

[0117] The computer system 801 may also include special purpose logicdevices (e.g., application specific integrated circuits (ASICs)) orconfigurable logic devices (e.g., simple programmable logic devices(SPLDs), complex programmable logic devices (CPLDs), and fieldprogrammable gate arrays (FPGAs)).

[0118] The computer system 801 may also include a display controller 809coupled to the bus 802 to control a display 810, such as a cathode raytube (CRT), for displaying information to a computer user. The computersystem includes input devices, such as a keyboard 811 and a pointingdevice 812, for interacting with a computer user and providinginformation to the processor 803. The pointing device 812, for example,may be a mouse, a trackball, or a pointing stick for communicatingdirection information and command selections to the processor 803 andfor controlling cursor movement on the display 810. In addition, aprinter may provide printed listings of the data structures/informationshown in FIGS. 3 and 4, or any other data stored and/or generated by thecomputer system 801.

[0119] The computer system 801 performs a portion or all of theprocessing steps of the invention in response to the processor 803executing one or more sequences of one or more instructions contained ina memory, such as the main memory 804. Such instructions may be readinto the main memory 804 from another computer readable medium, such asa hard disk 807 or a removable media drive 808. One or more processorsin a multi-processing arrangement may also be employed to execute thesequences of instructions contained in main memory 804. In alternativeembodiments, hard-wired circuitry may be used in place of or incombination with software instructions. Thus, embodiments are notlimited to any specific combination of hardware circuitry and software.

[0120] As stated above, the computer system 801 includes at least onecomputer readable medium or memory for holding instructions programmedaccording to the teachings of the invention and for containing datastructures, tables, records, or other data described herein. Examples ofcomputer readable media are compact discs, hard disks, floppy disks,tape, magneto-optical disks, PROMs (EPROM, EEPROM, flash EPROM), DRAM,SRAM, SDRAM, or any other magnetic medium, compact discs (e.g., CD-ROM),or any other optical medium, punch cards, paper tape, or other physicalmedium with patterns of holes, a carrier wave (described below), or anyother medium from which a computer can read.

[0121] Stored on any one or on a combination of computer readable media,the present invention includes software for controlling the computersystem 801, for driving a device or devices for implementing theinvention, and for enabling the computer system 801 to interact with ahuman user (e.g., print production personnel). Such software mayinclude, but is not limited to, device drivers, operating systems,development tools, and applications software. Such computer readablemedia further includes the computer program product of the presentinvention for performing all or a portion (if processing is distributed)of the processing performed in implementing the invention.

[0122] The computer code devices of the present invention may be anyinterpretable or executable code mechanism, including but not limited toscripts, interpretable programs, dynamic link libraries (DLLs), Javaclasses, and complete executable programs. Moreover, parts of theprocessing of the present invention may be distributed for betterperformance, reliability, and/or cost.

[0123] The term “computer readable medium” as used herein refers to anymedium that participates in providing instructions to the processor 803for execution. A computer readable medium may take many forms, includingbut not limited to, non-volatile media, volatile media, and transmissionmedia. Non-volatile media includes, for example, optical, magneticdisks, and magneto-optical disks, such as the hard disk 807 or theremovable media drive 808. Volatile media includes dynamic memory, suchas the main memory 804. Transmission media includes coaxial cables,copper wire and fiber optics, including the wires that make up the bus802. Transmission media also may also take the form of acoustic or lightwaves, such as those generated during radio wave and infrared datacommunications.

[0124] Various forms of computer readable media may be involved incarrying out one or more sequences of one or more instructions toprocessor 803 for execution. For example, the instructions may initiallybe carried on a magnetic disk of a remote computer. The remote computercan load the instructions for implementing all or a portion of thepresent invention remotely into a dynamic memory and send theinstructions over a telephone line using a modem. A modem local to thecomputer system 801 may receive the data on the telephone line and usean infrared transmitter to convert the data to an infrared signal. Aninfrared detector coupled to the bus 802 can receive the data carried inthe infrared signal and place the data on the bus 802. The bus 802carries the data to the main memory 804, from which the processor 803retrieves and executes the instructions. The instructions received bythe main memory 804 may optionally be stored on storage device 807 or808 either before or after execution by processor 803.

[0125] The computer system 801 also includes a communication interface813 coupled to the bus 802. The communication interface 813 provides atwo-way data communication coupling to a network link 814 that isconnected to, for example, a local area network (LAN) 815, or to anothercommunications network 816 such as the Internet. For example, thecommunication interface 813 may be a network interface card to attach toany packet switched LAN. As another example, the communication interface813 may be an asymmetrical digital subscriber line (ADSL) card, anintegrated services digital network (ISDN) card or a modem to provide adata communication connection to a corresponding type of communicationsline. Wireless links may also be implemented. In any suchimplementation, the communication interface 813 sends and receiveselectrical, electromagnetic or optical signals that carry digital datastreams representing various types of information.

[0126] The network link 814 typically provides data communicationthrough one or more networks to other data devices. For example, thenetwork link 814 may provide a connection to a another computer througha local network 815 (e.g., a LAN) or through equipment operated by aservice provider, which provides communication services through acommunications network 816. In preferred embodiments, the local network814 and the communications network 816 preferably use electrical,electromagnetic, or optical signals that carry digital data streams. Thesignals through the various networks and the signals on the network link814 and through the communication interface 813, which carry the digitaldata to and from the computer system 801, are exemplary forms of carrierwaves transporting the information. The computer system 801 can transmitand receive data, including program code, through the network(s) 815 and816, the network link 814 and the communication interface 813.

[0127] The mechanisms and processes set forth in the present descriptionmay be implemented using a conventional general purpose microprocessorprogrammed according to the teachings in the present specification, aswill be appreciated to those skilled in the relevant art(s). Appropriatesoftware coding can readily be prepared by skilled programmers based onthe teachings of the present disclosure, as will also be apparent tothose skilled in the relevant art(s).

[0128] The present invention thus also includes a computer-based productwhich may be hosted on a storage medium and include instructions whichcan be used to program a computer to perform a process in accordancewith the present invention. This storage medium can include, but is notlimited to, any type of disk including floppy disks, optical disks,CD-ROMs, magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, flashmemory, magnetic or optical cards, or any type of media suitable forstoring electronic instructions.

[0129] Preferred embodiments of the invention are listed below:

[0130] A. A system for the production of hydrogen from hydrocarbon fuelsuch as natural gas, propane, naphtha, and other hydrocarbons low insulfur content (<100 ppm sulfur by mass); wherein the product hydrogenis made substantially pure (>99.99%) by separating impurities using apressure swing adsorption (PSA) system, wherein no pretreatment of thefuel feed to the steam reformer by the removal of sulfur and molecularoxygen is carried out.

[0131] B. The hydrogen production system of A wherein the steamreforming catalyst is insensitive to sulfur and molecular oxygen,preferably the catalyst active metal comprises one or more of thefollowing group VIIIB metals singly or in combination; ruthenium,iridium, rhodium, platinum and palladium supported upon a high areaceramic support.

[0132] C. The hydrogen production system of A wherein the operation ofthe system is in a mesobaric regime, between 4 and 18 atmospheres, morepreferably the pressure is between 5 atm and 15 atm, most preferably thepressure is between 10 atm and 15 atm.

[0133] D. The hydrogen production system of A wherein feedback controlis employed for the delivery of fuel and or air to a catalytic combustorin proportion such that the peak temperature of the gases entering theprimary steam reformer does not exceed a safe maximum temperaturedetermined by the metallurgy of the steam reformer.

[0134] E. The hydrogen production system of A where no low temperaturewater gas shift reactor is employed, wherein the exit temperature of thehigh temperature water gas shift reactor employed is preferably above200° C., more preferably the temperature is greater than 250° C. andless than 400° C., most preferably the temperature is greater than 275°C. and less than 350° C.

[0135] F. The hydrogen production system of A wherein feedback controlof product carbon monoxide, or other impurity, concentration isemployed.

[0136] G. The hydrocarbon production system of A wherein thepretreatment includes at least one selected from the group includingpartial oxidation, hydrodesulfurization, adsorption, and absorption.

[0137] I. A hydrogen production method, which includes the catalyticsteam reforming and subsequent high temperature water gas shift oflow-sulfur (<100 ppm by mass) hydrocarbon fuels to produce hydrogenfollowed by hydrogen purification with pressure swing adsorption (PSA).

[0138] Having now fully described the invention, it will be apparent toone of ordinary skill in the art that many changes and modifications maybe made thereto, without departing from the spirit or scope of theinvention as set forth herein.

[0139] It is therefore to be understood that within the scope of theappended claims, the invention may be practiced otherwise than asspecifically described herein.

[0140] U.S. Provisional Application No. 60/214,737, filed Jun. 29, 2000,is hereby incorporated by reference in its entirety, the same as if setforth at length.

[0141] The entire contents of each of the above-mentioned patents,references and published applications is hereby incorporated byreference, the same as if set forth at length.

1. A reactor, comprising: a unitary shell assembly having an inlet andan outlet; a flow path extending within said shell assembly from saidinlet to said outlet, said flow path having a steam reformer sectionwith a first catalyst and a water gas shift reactor section with asecond catalyst, said steam reformer section being located upstream ofsaid water gas shift reactor section; a heating section within saidshell assembly and configured to heat said steam reformer section; and acooling section within said shell assembly and configured to cool saidwater gas shift reactor section.
 2. The reactor of claim 1, wherein saidflow path includes a preheat section located upstream of said steamreformer section.
 3. The reactor of claim 2, wherein said preheatsection includes a packing material.
 4. The reactor of claim 3, whereinsaid packing material is a sulfur absorbent bed.
 5. The reactor of claim1, wherein said flow path includes an adiabatic water gas shift reactorsection located downstream of said water gas shift reactor section. 6.The reactor of claim 1, wherein: said steam reformer section and saidwater gas shift reactor section are formed of an array of tubes; saidflow path includes an inlet tube header located upstream of said steamreformer section; and said flow path includes an outlet tube headerlocated downstream of said water gas shift reactor section.
 7. Thereactor of claim 6, wherein the interior of the tubes is provided with acatalyst in the form of at least one selected from the group consistingof a coating, a monolith, a loose packing of pellets, extrudates, andmixtures thereof.
 8. The reactor of claim 1, wherein said shell assemblyincludes: a means of thermal expansion relief; at least one inlet tosaid cooling section configured to receive a cooling medium; and atleast one outlet for said cooling section.
 9. The reactor of claim 8,wherein said shell assembly includes: at least one inlet to said heatingsection configured to receive a heating medium; and at least one outletfor said heating section.
 10. The integral reactor of claim 6, whereinsaid tubes in said array of tubes have an exterior surface configured toaid heat transfer between said heating section and said steam reformersection, and between said cooling section and said water gas shiftreactor section.
 11. The reactor of claim 10, wherein said exteriorsurface of said tubes are configured with at least one configurationselected from the group consisting of twisted tubes, finned tubes,rifled tubes, plate fins, loose packing material, and combinationsthereof.
 12. The reactor of claim 6, further comprising baffles withinsaid shell assembly and provided exterior of said tubes, said bafflesbeing configured to force a heat transfer medium flowing outside saidtubes across the array of tubes in a direction substantially normal to alongitudinal axis of said tubes.
 13. The reactor of claim 12, whereinsaid baffles have a modified surface area.
 14. The reactor of claim 1,further comprising a catalytic burner configured to heat at least one ofa heating medium provided within said heating section and a coolingmedium provided within said cooling section.
 15. The reactor of claim14, wherein said catalytic burner is provided within said shellassembly.
 16. The reactor of claim 14, wherein said catalytic burnerincludes at least one inlet for fuel delivery.
 17. The reactor of claim14, wherein said catalytic burner includes at least one selected fromthe group consisting of a means for mixing fuel and heated air, a meansfor preheating and/or igniting, at least one temperature sensor, andcombinations thereof.
 18. The reactor of claim 1, wherein said firstcatalyst is substantially resistant to poisoning by sulfur and molecularoxygen.
 19. The reactor of claim 1, wherein said second catalyst issubstantially resistant to poisoning by sulfur.
 20. The reactor of claim1, further comprising: an insulation assembly provided on at least aportion of an exterior of said shell assembly; and an outer housingprovided on an exterior of said insulation assembly.
 21. The reactor ofclaim 1, further comprising a second flow path defined by said coolingsection and said heating section, wherein said cooling section and saidheating section are fluidly connected.
 22. The reactor of claim 1,wherein said unitary shell assembly is a pressurized shell assembly. 23.The reactor of claim 1, wherein said unitary shell assembly is agas-tight shell assembly.
 24. The reactor of claim 1, wherein said shellassembly further comprises an insulating layer.
 25. The reactor of claim24, wherein said insulating layer is contiguous or noncontiguous. 26.The reactor of claim 1, wherein said first and second catalysts are thesame or different.
 27. The reactor of claim 1, wherein said firstcatalyst is in admixture with said second catalyst.
 28. The reactor ofclaim 1, wherein said second catalyst is in admixture with said firstcatalyst.
 29. The reactor of claim 1, wherein said shell assemblycomprises a plurality of inlets.
 30. The reactor of claim 1, whereinsaid shell assembly comprises a plurality of outlets.
 31. The reactor ofclaim 1, wherein said shell assembly comprises a tube side and a shellside.
 32. The reactor of claim 31, wherein said tube side forms acontinuous pressure vessel.
 33. A reactor for the production of hydrogenfrom at least one selected from the group consisting of natural gas,propane, liquefied petroleum gas, alcohols, naphtha, hydrocarbon fuelsand mixtures thereof, said reactor comprising: a unitary shell assemblyhaving an inlet and an outlet; a flow path extending within said shellassembly from said inlet to said outlet, said flow path including aconvectively-heated catalytic steam reformer and a convectively-cooledwater gas shift reactor.
 34. A method for producing hydrogen, comprisingthe step of: feeding at least one fuel selected from the groupconsisting of natural gas, propane, liquefied petroleum gas, alcohols,naphtha, hydrocarbon fuels and mixtures thereof, into a reactorcomprising a unitary shell assembly having an inlet and an outlet, and aflow path extending within the shell assembly from the inlet to theoutlet, the flow path comprising a convectively-heated catalytic steamreformer and a convectively-cooled water gas shift reactor, wherebyhydrogen is produced.
 35. A method for producing hydrogen from at leastone fuel selected from the group consisting of hydrocarbon fuel, naturalgas, propane, naphtha, hydrocarbons with <100 ppm sulfur by mass, andmixtures thereof, comprising: producing hydrogen by steam reforming saidfuel; and substantially purifying said hydrogen with a pressure swingadsorption (PSA) system; wherein prior to said producing, nopretreatment of said fuel to remove at least one impurity selected fromthe group consisting of sulfur and molecular oxygen and mixtures therofis carried out.
 36. The method of claim 35, wherein said steam reformingcomprises a steam reforming catalyst, and wherein said steam reformingcatalyst is insensitive to sulfur and molecular oxygen.
 37. The methodof claim 36, wherein said steam reforming catalyst comprises acatalytically active metal selected from the group consisting of groupVIIIB metals, ruthenium, iridium, rhodium, platinum, palladium andmixtures thereof supported upon a ceramic support.
 38. The method ofclaim 35, which is carried out at a pressure of between 4 and 18atmospheres.
 39. The method of claim 35, further comprising a feedbackcontrol loop for delivering said fuel or air or both to said steamreforming and for controlling a temperature of said fuel or air or both.40. The method of claim 35, which does not comprise a low temperaturewater gas shift reaction.
 41. The method of claim 40, furthercomprising, prior to said purifying and subsequent to said steamreforming, a high temperature water gas shift reaction, and wherein anexit temperature of a product exiting said high temperature water gasshift reaction is above 200° C.
 42. The method of claim 35, wherein saidreforming produces carbon monoxide or at least one impurity or both, andwherein said method further comprises a feedback control loop forcontrolling a concentration of said carbon monoxide or said impurity orboth.
 43. The method of claim 35, wherein said pretreatment is at leastone selected from the group consisting of partial oxidation,hydrodesulfurization, adsorption, absorption, and combinations thereof.